The idea would be to serve as a seed nursery for this seed company, am I reading this correctly? Is clubroot a problem in beets in your region?.....I have only heard of the clubroot pathogen, Plasmodiophora brassicae, infecting cabbage-type crops and relatives. But I appreciate that your concerns may be directed towards what the beet
roots provided by the seed company would have as contaminants that may enter your soil. The plasmodiophorid type pathogens can be pretty long-lived in your soil, so it's worth careful consideration. Depending on how quickly you need an
answer, you may be able to have the seed company do a quick test of clubroot "suppressiveness" by your soil: Have the seed company take some shavings from the surface of a few roots, mix into their own soil and as a parallel test, mix some of these shavings into your own soil. Into this soil, plant some brassica crop (kale, cabbage, turnip, etc.) that would normally be susceptible to clubroot and would normally exhibit good clubroot disease symptoms. After the seedlings that sprout have grown for sufficient time as to develop disease, pull up the plants and compare those from their soil to those grown in your soil. If the seedlings grown in your soil (+beet
root shavings) are disease-free or relatively so, then it may be that the microbes in your soil are "suppressive" against clubroot disease and you may be okay. But if they develop symptoms of clubroot and it can be traced back to the beet shavings, then you may be introducing a bit of a headache into your garden.
For a recent open-access discussion on the biological control of clubroot disease by microbes, see
https://link.springer.com/article/10.1007/s10658-023-02701-3
Good luck!